Hundreds were feared dead in the blast and dozens of injured people lined the streets covered in blood, as thick black smoke billowed overhead.

There were reports of workers trapped inside buildings.

The Norwegian prime minister Jens Stoltenberg was moved to a secret location and told the nation that the situation was “very serious”.

Seven people were later confirmed to have died in the explosion.

The tangled wreckage of a vehicle outside one of the government buildings indicated that it may have been a car bomb – the suspicion was confirmed by Norwegian police nearly two hours later. Early suggestions that it could have been a gas explosion were dismissed after it emerged that there was no gas network in central Oslo.

Extremist group Ansar al-Jihad al-Alami (Helpers of Global Jihad) was quick to claim responsibility for the bombing, calling it "revenge” for Norway’s occupation of Afghanistan and insults to the Prophet Mohammed.

This was a far cry from the actual perpetrator, named as Norwegian national Anders Behring Breivik who later claimed in a 1518-page manifesto that he had carried out the twin attacks as part of a crusade against multiculturalism and Islam.

Teenagers who survived the initial attack threw themselves into the sub-zero waters of the lake in an attempt to flee. Others hid under corpses and barricaded themselves inside their rooms. One 15-year-old girl managed to survive by crouching under the same rock the killer was standing on. Others played dead. A local man used his boat to save teenagers from the lake but had to decide who to save and who to leave as there were just too many people swimming in the water.

Once in police custody, Anders Breivik told police that the point of the massacre was to stop future recruitment of the Labour Party and send a sharp signal to the people. The nation's response was to fight harder for democracy.

Breivik was held in solitary confinement prior to his trial. He was appointed Geir Lippestad as his lawyer, who had in the past defended a neo-Nazi.

After the attacks, Breivik's manifesto - 2083 A European Declaration of Independence - proved an important tool for police where Breivik claimed links to the far-right English Defence League and a mentor called Richard from an offshoot of the Knights Templar.